U.S. patent number 10,277,129 [Application Number 15/825,638] was granted by the patent office on 2019-04-30 for switching overlap avoidance system for controlling power supply system.
This patent grant is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. The grantee listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Arvind Govindaraj, Jun Kikuchi.
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United States Patent |
10,277,129 |
Govindaraj , et al. |
April 30, 2019 |
Switching overlap avoidance system for controlling power supply
system
Abstract
A method includes controlling a power supply system to avoid an
over-voltage event across one or more switching devices of the
power supply system. The controlling is based on switching overlap
information that includes instructions for either advancing or
retarding a switching signal associated with at least one of the
switching devices.
Inventors: |
Govindaraj; Arvind (Saginaw,
MI), Kikuchi; Jun (Novi, MI) |
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC |
Dearborn |
MI |
US |
|
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Assignee: |
FORD GLOBAL TECHNOLOGIES, LLC
(Dearborn, MI)
|
Family
ID: |
53045696 |
Appl.
No.: |
15/825,638 |
Filed: |
November 29, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20180083537 A1 |
Mar 22, 2018 |
|
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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14088687 |
Nov 25, 2013 |
9853544 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60L
50/16 (20190201); B60L 3/003 (20130101); B60L
7/14 (20130101); B60L 50/61 (20190201); H02M
5/4585 (20130101); B60L 15/2054 (20130101); H02M
1/32 (20130101); H02M 3/158 (20130101); B60L
15/2009 (20130101); B60L 2240/486 (20130101); B60L
2210/10 (20130101); Y02T 10/70 (20130101); Y02T
10/62 (20130101); B60L 2240/443 (20130101); Y02T
10/72 (20130101); B60L 2240/12 (20130101); B60L
2240/441 (20130101); H02M 1/38 (20130101); Y02T
10/64 (20130101); Y02T 10/7072 (20130101); B60L
2210/40 (20130101); B60L 2240/423 (20130101); B60L
2240/421 (20130101) |
Current International
Class: |
H02M
3/158 (20060101); H02M 5/458 (20060101); B60L
3/00 (20190101); B60L 7/14 (20060101); H02M
1/32 (20070101); B60L 15/20 (20060101); H02M
1/38 (20070101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Finch, III; Fred E
Assistant Examiner: De Leon Domenech; Rafael O.
Attorney, Agent or Firm: Carlson, Gaskey & Olds
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation of U.S. patent application Ser. No.
14/088,687, which was filed on Nov. 25, 2013.
Claims
What is claimed is:
1. A method, comprising: controlling a power supply system to avoid
an over-voltage event across one or more switching devices of the
power supply system, the controlling step based on switching
overlap information that includes instructions for advancing one or
more pulse edges of a switching signal associated with at least one
of the switching devices, wherein the switching signal includes
multiple sets of rising edges and falling edges, wherein advancing
the one or more pulse edges of the switching signal includes
advancing a first rising edge or a first falling edge, but not
both, of a first set of the multiple sets.
2. The method as recited in claim 1, comprising not modifying the
switching signal if there is no risk of the over-voltage event.
3. The method as recited in claim 1, wherein the controlling step
includes: advancing a first pulse edge of the switching signal; and
delaying a second pulse edge of the switching signal.
4. The method as recited in claim 3, wherein a third pulse edge of
the switching signal is neither advanced nor delayed.
5. The method as recited in claim 1, wherein the controlling step
includes: determining a location of the one or more pulse edges of
the switching signal; and checking whether additional pulse edges
are scheduled to occur in the vicinity of the one or more pulse
edges of the switching signal.
6. The method as recited in claim 5, comprising invoking a pulse
edge repositioning routine if the additional pulse edges are
scheduled in the vicinity of the pulse edges of the switching
signal.
7. The method as recited in claim 1, comprising assigning a
priority system in order to select which of a plurality of
switching signals should be reconstructed.
8. The method as recited in claim 7, comprising adjusting the
switching signal having the lowest priority and leaving the
switching signal having the highest priority unaltered.
9. The method as recited in claim 1, wherein controlling the power
supply system includes calculating the next upcoming switching
instant for each leg of the power supply system based on an updated
duty cycle value and a half carrier cycle period.
10. The method as recited in claim 1, comprising prioritizing one
switching signal over another based on sensor readings or channel
propagation characteristics when determining which switching signal
should be advanced.
11. The method as recited in claim 1, wherein the controlling step
includes: determining whether the one or more pulse edges that are
advanced cause an unintended switching overlap; and if so,
repositioning the one or more pulse edges that were previously
advanced.
12. A method, comprising: controlling a power supply system of a
vehicle by automatically readjusting a switching signal in response
to a switching overlap between two or more switching devices of the
power supply system when a voltage spike exceeds a voltage rating
of at least one of the two or more switching device, wherein the
switching signal includes multiple sets of rising edges and falling
edges, wherein automatically readjusting the switching signal
includes advancing a first rising edge or a first falling edge, but
not both, of a first set of the multiple sets or altering an amount
of time between the first rising edge and the first falling edge of
the first set of the multiple sets.
13. The method as recited in claim 12, wherein the controlling step
includes: advancing a first pulse edge of the switching signal; and
delaying a second pulse edge of the switching signal.
14. The method as recited in claim 13, comprising the step of
ignoring a third pulse edge of the switching signal.
15. The method as recited in claim 12, comprising assigning a
priority system in order to select which of a plurality of
switching signals should be reconstructed.
16. The method as recited in claim 12, wherein the controlling step
includes: determining a location of pulse edges of the switching
signal; and checking whether additional pulse edges are scheduled
to occur in the vicinity of the pulse edges of the switching
signal.
17. A method, comprising: controlling a power supply system to
avoid an over-voltage event across one or more switching devices of
the power supply system, the controlling step based on switching
overlap information that includes instructions for advancing one or
more pulse edges of a switching signal associated with at least one
of the switching devices, wherein the switching signal includes
multiple sets of rising edges and falling edges, wherein advancing
the one or more pulse edges of the switching signal includes
altering an amount of time between a first rising edge and a first
falling edge of a first set of the multiple sets.
Description
TECHNICAL FIELD
This disclosure relates to an electrified vehicle, and more
particularly, but not exclusively, to a switching overlap avoidance
system and method for avoiding an over-voltage event across one or
more switching devices of a power supply system.
BACKGROUND
Hybrid electric vehicles (HEV's), plug-in hybrid electric vehicles
(PHEV's), battery electric vehicles (BEV's), fuel cell vehicles and
other known electrified vehicles differ from conventional motor
vehicles in that they are powered by one or more electric machines
(i.e., electric motors and/or generators) instead of or in addition
to an internal combustion engine. High voltage and high current are
typically supplied to the electric machines by one or more
batteries that store electrical power.
Electrified vehicles typically employ power supply systems that
support bi-directional power flow within the vehicle. The power
supply systems include a plurality of switching devices that
perform switching operations according to a drive signal produced
by a controller to control a load. For example, electrified
vehicles often include inverter/converter systems that utilize a
plurality of semiconductor switching devices, such as power
metal-oxide semiconductor field effect transistors (MOSFET's) or
insulated gate bipolar transistors (IGBT's), that selectively
undergo switching operations for powering one or more AC drive
motors from a DC storage battery, or alternatively, to charge the
DC storage battery from an AC source, such as a generator.
An over-voltage event can be caused by various factors, such as
voltage-control delay and voltage sensor offset error, and may
occur when a switching device of the power supply system undergoes
switching operations between ON and OFF. This voltage-spike occurs
due to the effect of a large rate of change of current during a
switching event, i.e. di/dt, and parasitic inductance L (which can
be formulated as V=Ldi/dt).
The voltage spike issue described above may become more significant
with modern power switching devices, which are generally capable of
faster turn-on and turn-off (i.e., large di/dt). Switching power
converters are typically designed to include a relatively large
voltage margin so that such voltage spike can be maintained below
the voltage rating of the switching device. However, in the case of
multi-leg switching power converters, such as three-phase PWM
inverters commonly used in utility, consumer and automotive
applications, simultaneous switching events among two or more legs
may lead to relatively large voltage spike across an individual
device. This can result in relatively poor voltage rating
utilization for multi-leg switching power converters.
SUMMARY
A method according to an exemplary aspect of the present disclosure
includes, among other things, controlling a power supply system to
avoid an over-voltage event across one or more switching devices of
the power supply system, the controlling step based on switching
overlap information that includes instructions for either advancing
or retarding a switching signal associated with at least one of the
switching devices.
In a further non-limiting embodiment of the foregoing method, the
method includes the step of not modifying the switching signal if
there is no risk of the over-voltage event.
In a further non-limiting embodiment of either of the foregoing
methods, the step of advancing or retarding the switching signal
includes advancing or retarding one or more pulse edges of the
switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the switching overlap information includes an estimate of
a likelihood for a switching overlap to occur between two or more
switching signals.
In a further non-limiting embodiment of any of the foregoing
methods, the controlling step includes advancing a first pulse edge
of the switching signal and delaying a second pulse edge of the
switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, a third pulse edge of the switching signal is neither
advanced nor delayed.
In a further non-limiting embodiment of any of the foregoing
methods, the controlling step includes advancing pulse edges of the
switching signal or retarding pulse edges of the switching
signal.
In a further non-limiting embodiment of any of the foregoing
methods, the controlling step includes determining a location of
pulse edges of the switching signal and checking whether additional
pulse edges are scheduled to occur in the vicinity of the pulse
edges of the switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the method includes invoking a pulse edge repositioning
routine if the additional pulse edges are scheduled in the vicinity
of the pulse edges of the switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the method includes assigning a priority system in order
to select which of a plurality of switching signals should be
reconstructed.
A method according to another exemplary aspect of the present
disclosure includes among other things, controlling a power supply
system of a vehicle to avoid an over-voltage event across one or
more switching devices of the power supply system by readjusting a
switching signal in response to a switching overlap between two or
more of the switching devices.
In a further non-limiting embodiment of the foregoing method, the
over-voltage event includes a voltage spike that exceeds a voltage
rating of the one or more switching devices.
In a further non-limiting embodiment of either of the foregoing
methods, readjusting the switching signal includes advancing a
pulse edge of the switching signal or retarding the pulse edge of
the switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the method includes ignoring the switching overlap if
there is no risk of the over-voltage event.
In a further non-limiting embodiment of any of the foregoing
methods, the controlling step includes advancing a first pulse edge
of the switching signal and delaying a second pulse edge of the
switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the method includes the step of ignoring a third pulse
edge of the switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the switching overlap occurs when a first pulse edge of
the switching signal occurs at the same time as a second pulse edge
of a second switching signal.
In a further non-limiting embodiment of any of the foregoing
methods, the method includes assigning a priority system in order
to select which of a plurality of switching signals should be
reconstructed.
In a further non-limiting embodiment of any of the foregoing
methods, the controlling step includes determining a location of
pulse edges of the switching signal and checking whether additional
pulse edges are scheduled to occur in the vicinity of the pulse
edges of the switching signal.
A power supply system according to another exemplary aspect of the
present disclosure includes, among other things, a plurality of
switching devices and a switching overlap avoidance system that
monitors switching events of the plurality of switching devices,
the switching overlap avoidance system configured to readjust one
or more switching signals in response to a switching overlap
between two or more of the plurality of switching devices in order
to avoid an over-voltage event.
The embodiments, examples and alternatives of the preceding
paragraphs, the claims, or the following description and drawings,
including any of their various aspects or respective individual
features, may be taken independently or in any combination.
Features described in connection with one embodiment are applicable
to all embodiments, unless such features are incompatible.
The various features and advantages of this disclosure will become
apparent to those skilled in the art from the following detailed
description. The drawings that accompany the detailed description
can be briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates a powertrain of an electrified
vehicle.
FIG. 2 illustrates a topology of a power supply system.
FIG. 3 illustrates a switching overlap avoidance system that can be
used to control the power supply system of FIG. 2.
FIGS. 4A and 4B are graphical representations of switching signals
measured over time that control switching operations of a power
supply system.
FIGS. 5A, 5B, 5C and 5D schematically illustrate a method for
detecting switching signal overlaps using the switching overlap
avoidance system of FIG. 3.
FIG. 6 schematically illustrates a priority system of the switching
overlap avoidance system of FIG. 3.
DETAILED DESCRIPTION
This disclosure relates to a switching overlap avoidance system and
method for controlling a power supply system of an electrified
vehicle. The inventive system predicts a switching overlap between
two or more switching devices and modifies a switching signal
associated with at least one of the switching devices in response
to the detected switching overlap. The switching signals may be
readjusted by advancing or retarding pulse edges, which represent
turn on/turn off transients, in order to avoid an over-voltage
event across one or more switching devices. A switching overlap
identified by concurrent switching pulse edges can alternatively be
ignored if there is no risk of an over-voltage event. These and
other features are discussed in greater detail herein.
FIG. 1 schematically illustrates a powertrain 10 for an electrified
vehicle 12, such as a HEV. Although depicted as a HEV, it should be
understood that the concepts described herein are not limited to
HEV's and could extend to other electrified vehicles, including but
not limited to, PHEV's, BEV's, and fuel cell vehicles.
In one embodiment, the powertrain 10 is a power split system that
employs a first drive system that includes a combination of an
engine 14 and a generator 16 (i.e., a first electric machine) and a
second drive system that includes at least a motor 36 (i.e., a
second electric machine), the generator 16 and a battery 50. For
example, the motor 36, the generator 16 and the battery 50 may make
up an electric drive system 25 of the powertrain 10. The first and
second drive systems generate torque to drive one or more sets of
vehicle drive wheels 30 of the electrified vehicle 12.
The engine 14, such as an internal combustion engine, and the
generator 16 may be connected through a power transfer unit 18. In
one non-limiting embodiment, the power transfer unit 18 is a
planetary gear set. Of course, other types of power transfer units,
including other gear sets and transmissions, may be used to connect
the engine 14 to the generator 16. The power transfer unit 18 may
include a ring gear 20, a sun gear 22 and a carrier assembly 24.
The generator 16 is driven by the power transfer unit 18 when
acting as a generator to convert kinetic energy to electrical
energy. The generator 16 can alternatively function as a motor to
convert electrical energy into kinetic energy, thereby outputting
torque to a shaft 26 connected to the carrier assembly 24 of the
power transfer unit 18. Because the generator 16 is operatively
connected to the engine 14, the speed of the engine 14 can be
controlled by the generator 16.
The ring gear 20 of the power transfer unit 18 may be connected to
a shaft 28 that is connected to vehicle drive wheels 30 through a
second power transfer unit 32. The second power transfer unit 32
may include a gear set having a plurality of gears 34A, 34B, 34C,
34D, 34E, and 34F. Other power transfer units may also be suitable.
The gears 34A-34F transfer torque from the engine 14 to a
differential 38 to provide traction to the vehicle drive wheels 30.
The differential 38 may include a plurality of gears that enable
the transfer of torque to the vehicle drive wheels 30. The second
power transfer unit 32 is mechanically coupled to an axle 40
through the differential 38 to distribute torque to the vehicle
drive wheels 30.
The motor 36 can also be employed to drive the vehicle drive wheels
30 by outputting torque to a shaft 46 that is also connected to the
second power transfer unit 32. In one embodiment, the motor 36 and
the generator 16 are part of a regenerative braking system in which
both the motor 36 and the generator 16 can be employed as motors to
output torque. For example, the motor 36 and the generator 16 can
each output electrical power to a high voltage bus 48 and the
battery 50. The battery 50 may be a high voltage battery that is
capable of outputting electrical power to operate the motor 36 and
the generator 16. Other types of energy storage devices and/or
output devices can also be incorporated for use with the
electrified vehicle 12.
The motor 36, the generator 16, the power transfer unit 18, and the
power transfer unit 32 may generally be referred to as a transaxle
42, or transmission, of the electrified vehicle 12. Thus, when a
driver selects a particular shift position, the transaxle 42 is
appropriately controlled to provide the corresponding gear for
advancing the electrified vehicle 12 by providing traction to the
vehicle drive wheels 30.
The powertrain 10 may additionally include a control system 44 for
monitoring and/or controlling various aspects of the electrified
vehicle 12. For example, the control system 44 may communicate with
the electric drive system 25, the power transfer units 18, 32 or
other components to monitor and/or control the electrified vehicle
12. The control system 44 includes electronics and/or software to
perform the necessary control functions for operating the
electrified vehicle 12. In one embodiment, the control system 44 is
a combination vehicle system controller and powertrain control
module (VSC/PCM). Although it is shown as a single hardware device,
the control system 44 may include multiple controllers in the form
of multiple hardware devices, or multiple software controllers
within one or more hardware devices.
A controller area network (CAN) 52 allows the control system 44 to
communicate with the transaxle 42. For example, the control system
44 may receive signals from the transaxle 42 to indicate whether a
transition between shift positions is occurring. The control system
44 could also communicate with a battery control module of the
battery 50, or other control devices.
Additionally, the electric drive system 25 may include one or more
controllers 54, such as an inverter system controller (ISC). The
controller 54 is configured to control specific components within
the transaxle 42, such as the generator 16 and/or the motor 36,
such as for supporting bidirectional power flow. In one embodiment,
the controller 54 is an inverter system controller combined with a
variable voltage converter (ISC/VVC).
FIG. 2 illustrates a power supply system 60 that can be
incorporated into an electrified vehicle. For example, the power
supply system 60 may include an inverter system, a converter
system, or a combined voltage converter/inverter of the electrified
vehicle 12 of FIG. 1. In one embodiment, the power supply system 60
includes a motor-drive inverter, a generator-drive inverter and a
variable voltage converter (VVC). The power supply system 60
outputs power for controlling loads, such as a motor 36 and a
generator 16, by switching one or more switching devices 62.
In one embodiment, the power supply system 60 includes multiple
switching devices 62. The switching devices 62 may undergo
switching operations (i.e., toggling between ON and OFF) to power
the loads using energy from the battery 50, or alternatively, to
charge the battery 50 over a DC bus 64. In one embodiment, the
switching devices 62 are IGBT's. In another embodiment, the
switching devices 62 are power MOSFET's. Other switching devices
and other configurations of the power supply system 60 are
contemplated as within the scope of this disclosure.
The power supply system 60 may include multiple legs 66 of
switching devices 62 that are connected in parallel. Each leg 66
includes first and second switching devices 62.sub.a,b,c,d,e,f,g-1,
62.sub.a,b,c,d,e,f,g-2 connected in series, respectively. The
number of legs 66 provided may correspond to the total number of
phases of the loads and sources, which is in one embodiment a three
phase motor 36, a three phase generator 16 and a battery 50.
Accordingly, in one embodiment, the power supply system 60 includes
seven legs 66a, 66b, 66c, 66d, 66e, 66f and 66g of switching
devices 62 for controlling the power flow among the loads and the
source. It should however be appreciated that the power supply
system 60 could include any number of legs of switching devices for
powering loads having any number of phases.
In one embodiment, the switching devices 62.sub.a,b,c,d,e,f,g-1,
62.sub.a,b,c,d,e,f,g-2 of each leg 66a to 66g may be alternatively
switched between ON and OFF positions to convert DC power to three
phase AC power to drive the motor 36 and the generator 16, or to
convert to a different voltage-level of DC power to the high
voltage battery 50. A switching overlap can occur during the
switching events of the various switching devices 62, which can
lead to an over-voltage event (i.e., a voltage spike that exceeds
the voltage rating of the switching device 62) across one or more
of the switching devices 62. As discussed in greater detail below,
an exemplary system and method for predicting switching overlap and
readjusting switching signals to avoid the switching overlap can be
used to control the power supply system 60 and thereby avoid
over-voltage events.
FIG. 3 illustrates a switching overlap avoidance system 70 that can
be used to control the power supply system 60 of FIG. 2. In one
embodiment, the switching overlap avoidance system 70 is part of a
controller 72 of the power supply system 60. As can be appreciated,
in one embodiment, the switching overlap avoidance system 70 is
implemented as software on the controller 72. For example, the
switching overlap avoidance system 70 may employ one or more
algorithms programmed into the controller 72 in order to predict
and avoid switching overlaps. Alternatively, in another embodiment,
the switching overlap avoidance system 70 could be implemented as
custom designed hardware circuitry of the power supply system
60.
The exemplary switching overlap avoidance system 70 includes a
master clock 74, a pulse-width modulation (PWM) block 76, a
switching overlap detection block (SODB) 78, and a switching pulse
edge repositioning block (SPERB) 80. The master clock 74 provides a
time reference for the switching overlap avoidance system 70. In
one embodiment, the master clock 74 creates a stream of pulses that
are in the form of a square wave (see graph (a) of FIG. 5). Other
clock signal formats are also contemplated within the scope of this
disclosure.
The PWM block 76 generates switching signals P.sub.1 to P.sub.n for
controlling switching operations of the switching devices 62 of the
power supply system 60. The switching signals P.sub.1 to P.sub.n
are derived from the master clock 74 and may be generated as
integer multiples of the master clock 74 tick. The switching
signals P.sub.1 to P.sub.n include switching event information for
controlling the switching devices between ON and OFF positions.
In one embodiment, the SODB 78 can predict switching overlaps by
monitoring the PWM block 76 with a timing circuit driven by the
master clock 74. The SPERB 80 can then reschedule overlapping pulse
edges of the switching signals P.sub.1 to P.sub.n and communicate
readjusted switching signals P.sub.1' to P.sub.n' to the gate
drives of the switching devices 62. The SPERB 80 can reschedule one
or more of the switching signals P.sub.1 to P.sub.n by advancing or
retarding the pulse edges of these signals. The total pulse width
of the switching signals P.sub.1' to P.sub.n' may be impacted by
this readjustment. Between the SODB 78 and the SPERB 80, it is
ensured that the repositioned pulse edges of the switching signals
P.sub.1 to P.sub.n do not cause an unintended switching
overlap.
FIG. 4 (with continued reference to FIG. 3) schematically
illustrates the basic principle of operation of the switching
overlap avoidance system 70. The PWM block 76 may generate any
number of switching signals P.sub.1 to P.sub.n over a time t which
may be subsequently communicated to the gate drives of the
switching devices 62 for commanding various switching events. The
SODB 78 locates pulse edges 82 (i.e., rising edges or falling
edges) associated with each switching signal P.sub.1 to P.sub.n and
estimates whether there is likelihood for a switching overlap 84 to
occur between two or more of the switching signals P.sub.1 to
P.sub.n. The switching overlap 84 may occur when a pulse edge 82 of
one of the switching signals P.sub.1 to P.sub.n occurs at the same
time as another pulse edge 82 from another switching signal P.sub.1
to P.sub.n. This is shown in graph (a) of FIG. 4.
The switching overlap information may be communicated from the SODB
78 to the SPERB 80. If there is a potential for one or more
switching overlaps 84, the SPERB 80 is configured to readjust one
or more of the switching signals P.sub.1 to P.sub.n to eliminate
switching overlap. This is shown in graph (b) of FIG. 4. In one
embodiment, the SPERB 80 may readjust the switching signals P.sub.1
to P.sub.n by advancing or delaying the pulse edge(s) 82 associated
with one or more of the switching signals P.sub.1 to P.sub.n to
create readjusted switching signals P.sub.1' to P.sub.n'. Pulse
edges 82a and 82b of readjusted switching signal P.sub.n' are
examples of retarded signals and pulse edge 82c of readjusted
switching signal P2' is an example of a signal that has been
advanced because of a potential for a switching overlap. The
readjusted signals P.sub.1' to P.sub.n' avoid switching overlap
that can result in over-voltage events.
In another embodiment, if it is determined by the switching overlap
avoidance system 70 that a particular switching overlap 84 does not
present a risk of an over-voltage event, the switching overlap 84
can be ignored (see, for example, switching overlap 84a associated
with unchanged switching signal P.sub.1' and P.sub.n'). For
example, if the dc-bus voltage is low enough even when the
overlapped voltage spikes are taken into account, the switching
overlap event can be ignored because there is no concern to have an
overvoltage going beyond the power device voltage rating in such an
instance. Another non-limiting instance in which a switching
overlap 84 may be ignored is where the overlap occurs between a
switching event that is ending and a switching event that is
beginning. In yet another embodiment, any combination of advancing,
delaying or not changing the positioning of the pulse edges 82 may
be used to readjust the switching signals P.sub.1 to P.sub.n.
FIGS. 5 and 6, with continued reference to FIGS. 1-4, describe, in
greater detail, a method for controlling the power supply system 60
using the switching overlap avoidance system 70 described above.
Referring first to FIG. 5, the master clock 74 creates a stream of
pulses 88 (graph (a) of FIG. 5) and drives a counter C.sub.m (graph
(b) of FIG. 5), which may be part of the PWM block 76. The counter
C.sub.m increments every clock tick T.sub.c of the master clock 74
to provide a time reference for the switching overlap avoidance
system 70. In other words, the counter C.sub.m counts the stream of
pulses 88 generated by the master clock 74.
In one embodiment, it is assumed that the PWM block 76 produces a
center aligned asymmetrical modulation (switching) signal. However,
other PWM implementations are also contemplated within the scope of
this disclosure.
FIG. 5(c) illustrates how a PWM switching pulse for a particular
leg (i.e., one of the legs 66a, 66b, 66c, 66d, 66e, 66f and 66g of
FIG. 2) is generated in the PWM block 76 in FIG. 3. Each routine is
triggered at every peak and valley of the triangular PWM carrier
based on the assumption of the center-aligned asymmetric PWM
scheme. The PWM carrier is generated with an up-down counter which
is a part of the PWM block 76 driven by the master clock 74. A
specific half carrier cycle is employed, in one embodiment, and is
specified as R1 in FIG. 5(c). At the beginning of the half carrier
cycle, the duty-cycle (or equivalently, the PWM modulation signal)
is updated. The duty cycle value is the outcome of a current,
torque or predetermined control strategy. The PWM modulation signal
is compared with the PWM carrier and the switching moment for this
particular carrier half-cycle is determined. This routine repeats
cycle-by-cycle and a PWM pulse train is generated as shown in FIG.
5(d). This pulse can be interpreted as one of P.sub.1, P.sub.2, . .
. , P.sub.n in FIG. 2 and FIG. 3.
The same routine is applied to all the legs 66 of the power supply
system 60 of FIG. 2. In one embodiment, the SODB 78 calculates the
next up-coming switching instant based on the updated duty-cycle
value and the half carrier cycle period as follows:
T.sub.C1=D.sub.1*T.sub.p1 (1) where T.sub.p1=n*T.sub.c, n is an
integer value of the number of cycles corresponding to the half PWM
carrier cycle, and T.sub.c is the master clock period.
In another embodiment, the SODB 78 may calculate the next switching
instant by referring to the corresponding master clock 74 counter
value T.sub.C1. The SODB 78 compares the switching instants based
on the time-base provided by the master clock 74 counter C.sub.m,
and detects the possibility of switching overlap among two or more
multiple legs 66.
If a switching overlap is detected, the routine R.sub.1 may invoke
a pulse edge repositioning routine for readjusting one or more
switching signals. This routine is executed in the SPERB 80.
The SPERB 80 may function to reposition one or more pulse edges of
conflicting switching signals while trying to preserve the wave
shape of the switching signals. The pulse edge(s) may be either
advanced or retarded depending on the overall impact such changes
may have on the shape of the switching signals. Alternatively, a
pulse edge overlap could be ignored where it is determined by the
controller 72 that the switching device 62 is not at risk for an
over-voltage event. It is noted that over-voltage events generally
do not occur under low load currents or low dc-bus voltages.
In one embodiment, illustrated in FIG. 6, the SPERB 80 utilizes a
priority system 100 in order to select which switching signal(s)
should be readjusted. A priority value PPR.sub.1 to PPR.sub.n may
be assigned to each switching signal P.sub.1 to P.sub.n. In one
embodiment, the priority value PPR.sub.1 is given the highest
priority, whereas each subsequent priority value PPR.sub.2 to
PPR.sub.n is given a lower priority than the previous priority
value. The switching signals P with the lowest priority, such as
signal P.sub.n in this example, are the most likely to be
repositioned, whereas the highest priority signals (i.e., P.sub.1
in this example) will be unaltered. The priority of the signals may
be calculated and assigned to achieve the least amount of
distortion to the output current wave form of the switching signals
P.sub.1 to P.sub.n. The SPERB 80 could be programmed to store,
dynamically estimate/calculate, or otherwise access the priority
system 100 for use in reconstructing switching signals P.sub.1 to
P.sub.n in response to a switching overlap.
In one embodiment, the following information may be used to
calculate and assign the priority values PPR.sub.1 to PPR.sub.n: 1.
Current sensor readings; 2. Knowledge of the modulation strategy;
3. Bus bar geometry; and 4. Channel propagation characteristics. Of
course, other information may also be used to establish the
priority system 100.
Although the different non-limiting embodiments are illustrated as
having specific components or steps, the embodiments of this
disclosure are not limited to those particular combinations. It is
possible to use some of the components or features from any of the
non-limiting embodiments in combination with features or components
from any of the other non-limiting embodiments.
It should be understood that like reference numerals identify
corresponding or similar elements throughout the several drawings.
It should be understood that although a particular component
arrangement is disclosed and illustrated in these exemplary
embodiments, other arrangements could also benefit from the
teachings of this disclosure.
The foregoing description shall be interpreted as illustrative and
not in any limiting sense. A worker of ordinary skill in the art
would understand that certain modifications could come within the
scope of this disclosure. For these reasons, the following claims
should be studied to determine the true scope and content of this
disclosure.
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